1. Field of the Invention
The present invention generally relates to an input device and, more particularly, to a coordinate data input device comprising a pair of detecting members, each including a resistance film provided on the surface of an insulating substrate.
2. Description of the Related Art
Recently, a coordinate data input device for indicating two-dimensional coordinate data on a display screen, which can be operated by an analog data-entering operation through, e.g., an operator""s finger, has been widely used in digital data processors with displays incorporated therein, such as a personal computer, a word processor, an electronic notebook, etc. In particular, a coordinate data input device of a touch-sensitive type, adapted to be incorporated in the display such as LCD (a liquid crystal display) or CRT (a cathode-ray tube), or in a keyboard or a mouse provided in the data processors, has been known by the name of a touchscreen or a touchpad.
A conventional, touch-sensitive type coordinate data input device generally includes a pair of plate-like detecting members, each provided with an insulating substrate and a resistance film formed on the surface of the insulating substrate. The detecting members are mutually superimposed through a gap, with resistance films being opposed to each other. The gap between the detecting members is ensured by a large number of dot spacers arranged and distributed on the surface of the resistance film of one detecting member. The dot spacers serve to prevent the detecting members from being deformed due to a self-weight so as to maintain the gap between the detecting members, while permitting the resistance films to be shorted when at least one of detecting members is deformed under a pushing force.
Each detecting member is also provided with a pair of electrodes (or an electrode pair) respectively laid along opposed outer peripheral regions of the resistance film so as to be electrically connected with the latter. In the pair of superimposed detecting members, the electrode pairs thereof are located at angularly positions shifted by, generally, 90 degrees relative to each other. In this structure, a predetermined voltage is alternately applied to the resistance films between the pair of electrodes of each resistance film. In this state, when an operator pushes by, e.g., his finger a desired location of the outer surface of the insulating substrate of one detecting member, the resistance films are shorted to each other at the location of the pushed portion, and thereby a partial voltage corresponding to the location of the pushed portion is measured in the resistance film to which the voltage is not applied. In this way, partial voltages alternately generated in the respective resistance films are measured, and thereby the two-dimensional coordinate of the pushed location is determined.
The pair of electrodes in each detecting member are connected respectively with a pair of wiring strips which are arranged on the insulating substrate to be spaced from the resistance film. The electrodes and the wiring strips are normally patterned on the surface of the insulating substrate as a conductor. Generally, the insulating substrate of each detecting member includes a major part for carrying the resistance film and electrode pair, and an appendage part extending from the major part. The wiring strips in each detecting member are laid on the major and appendage parts of the insulating substrate, so as to be converged at the distal end of the appendage part, and are connected to external signal and power circuits through a connector. In this structure, a voltage is applied to the resistance film of each detecting member through the wiring strips and the electrode pair, and the partial voltages are measured as described above, whereby the coordinate data is entered.
In the touch-sensitive type coordinate data input device having above-described structure, if an electro-static discharge occurs on the detecting members, the discharge may penetrate inside the input device through the outer peripheral region of the superimposed pair of detecting members, and reach the conductors on the insulating substrates. As a result, a high voltage is instantaneously applied to the conductors, i.e., the electrodes and wiring strips, which may damage electronic parts such as an IC in the signal circuit connected with the wiring strips.
One solution for preventing the external circuit from being damaged due to the electro-static discharge can be provided, wherein an electric conductive plate connected to a ground is arranged in an equipment housing into which the coordinate data input device is incorporated, so as to be located along the outer peripheral region of the detecting members. According to this structure, the electro-static discharge occurs mainly on the conductive plate, and thereby the discharge may be prevented from penetrating inside the coordinate data input device. Another solution can also be provided, wherein the dimension of the insulating substrates of the detecting members is sufficiently enlarged in comparison with the resistance films so as to increase the distance between the outer peripheral edge of the insulating substrates and the conductors. In this structure, the electro-static discharge also hardly reaches the conductors. Alternatively, a clamp diode may be arranged between the wiring strips and the signal circuit, which can prevent the signal circuit from being damaged even when an electro-static discharge occurs on the conductors in the coordinate data input device.
However, the solution using the conductive plate or clamp diode may cause the problems in that the number of parts as well as the number of assembling steps, of the coordinate data input device as well as of an electronic equipment including the same, are increased, and thus a manufacturing cost significantly rises. On the other hand, if the dimension of the insulating substrates is enlarged to such an extent that the discharge on the conductor hardly occurs, it becomes difficult to ensure an installation space for the coordinate data input device particularly in a case where the device is a touch-sensitive type pointing device or a touchpad adapted to be incorporated in a keyboard or mouse.
It is, therefore, an object of the present invention to provide a coordinate data input device of a touch-sensitive type, having excellent resistance against an electro-static discharge, which can be readily produced without increasing the number of parts or assembling steps, so as to prevent a remarkable rise in manufacturing cost.
It is another object of the present invention to provide a coordinate data input device of a touch-sensitive type, which can provide excellent resistance against an electro-static discharge, without excessively enlarging the dimension of the device.
In order to accomplish the above objects, the present invention provides a coordinate data input device comprising a pair of detecting members, each of which includes an insulating substrate, a resistance film provided on the insulating substrate and a conductor formed on the insulating substrate to be electrically connected with the resistance film, the pair of detecting members being arranged in a face-to-face manner in that respective resistance films of the detecting members are opposed to each other; a spacer disposed between the pair of detecting members to define a gap between the respective resistance films, the spacer permitting the resistance films to be shorted with each other when at least one of the detecting members is deformed; and a ground conductor element disposed between the pair of detecting members, the ground conductor element substantially surrounding the resistance films and conductors of the detecting members.
In the above coordinate data input device, the ground conductor element may be formed as single electrically conductive line patterned on the insulating substrate of one of the detecting members.
Alternatively, the ground conductor element may be formed as a pair of electrically conductive lines respectively patterned on insulating substrates of the detecting members.
In this arrangement, it is preferred that the pair of electrically conductive lines are partially overlapped with each other.
Also, it is advantageous that an electrically conductive piece is interposed between overlapped portions of the pair of electrically conductive lines.
The electrically conductive piece may be made of an electrically conductive adhesive.
The insulating substrate of each of the detecting members may include a major part for carrying the resistance film and an appendage part extending from the major part, and insulating substrates of the detecting members may be integrally joined with each other through respective appendage parts.
In this arrangement, the conductor of each of the detecting members may be laid on the major part and continuously on the appendage part, and the ground conductor element may be laid on the major part and continuously on the appendage part of at least one of the detecting members.
The conductor of one of the detecting members may include a pair of first electrodes electrically connected with the resistance film of the one detecting member and a pair of first wiring strips extending respectively from the first electrodes and patterned on the insulating substrate of the one detecting member, and the conductor of the other of the detecting members may include a pair of second electrodes electrically connected with the resistance film of the other detecting member and a pair of second wiring strips extending respectively from the second electrodes and patterned on the insulating substrate of the other detecting member, the pair of first electrodes being oriented generally orthogonally to the pair of second electrodes.
Alternatively, the conductor of one of the detecting members may include a pair of first electrodes electrically connected with the resistance film of the one detecting member and a pair of first wiring strips extending respectively from the first electrodes and patterned on the insulating substrate of the one detecting member, and the conductor of the other of the detecting members may include a single electrode electrically connected with the resistance film of the other detecting member and a single second wiring strip extending from the second electrode and patterned on the insulating substrate of the other detecting member, the pair of first electrodes being oriented generally orthogonally to the second electrode.